1. Field of the Invention
The invention concerns a microwave generator comprising two coaxially arranged electrodes which are provided in a housing and which are separated by way of a spark gap, which sparks across when a high voltage is applied for the radiation of microwaves.
The functioning of such a microwave generator is based on a high voltage source being short-circuited across a spark gap and thus discharged. The high voltage source can have a capacitor array which is charged up in parallel on the basis of the principle of the Marx surge voltage circuit and which is then connected in series. As an alternative to using a Marx surge voltage circuit it is also possible to employ an explosive-operated high voltage generator, which, in comparison with conventional high voltage generators, can provide a single high voltage pulse with an extremely high level of pulse energy.
As a consequence of the short-circuiting of the high voltage source across the spark gap, strongly oscillating discharge or short-circuit currents with a steep edge occur, which involve a mix of very high frequencies which are radiated by way of a radiation element forming an antenna as microwave energy with a wide-band spectrum which is dependent on the frequency mix. That wide-band microwave spectrum has a very high level of energy density so that, in the area surrounding such a microwave generator, for example radio communication is at least adversely affected or input circuits of electronic circuit arrangements can be interfered with by virtue of resonance effects or in the extreme case can even be destroyed.
2. Discussion of the Prior Art
German Patent Application No. DE 101 51 565 A1 discloses a microwave generator which has a high voltage spark gap between axially alignedly arranged electrodes, wherein on both sides of the spark gap the electrodes and their coaxial holders are accompanied at least over a part of their axial longitudinal extent by an electrical conductor which extends in spaced relationship therewith and which is electrically conductingly connected to one of the electrodes. In that microwave generator the spark gap is formed between a small mushroom top-shaped electrode and a larger lobe-like electrode. The lobe-like electrode is surrounded by an outer conductor connected to the mushroom top-shaped electrode by way of a suitable connecting structure. That connecting structure, together with the mushroom top-shaped electrode, can be displaced by way of a spindle mechanism in respect of its axial position in relation to the stationary second electrode and the stationary conductor surrounding same, for tuning purposes.
Prior filed German Patent Application No 10 2005 002 279 discloses a microwave generator having a central electrode which at the front end has a radiating element and an external electrode which coaxially surrounds the central electrode along an axially extending resonator portion, wherein the two electrodes are of a rotationally symmetrical configuration and define a spark gap which sparks across when a high voltage is applied and radiates microwaves by way of the radiating element of the central electrode. That microwave generator substantially comprises the two metallic electrodes, namely the central electrode with the radiating element and the external electrode coaxially enclosing same, the electrodes defining the axially extending resonator portion of the microwave generator. The metallic electrodes are mounted to the mutually remote ends of an electrically insulating housing sleeve and can be charged up by simply contacting at the two axially mutually remote ends of the electrodes with a pulsed high voltage source. This involves what is referred to as a twin-wire feed. The interior of the housing sleeve, apart from the two electrodes, does not contain any further parts and components, which could adversely affect high voltage dielectric strength. To increase high voltage dielectric strength the internal space of the microwave generator can be filled with a gaseous or liquid dielectric. The gaseous dielectric is for example SF6.
In the microwave generator of the last-mentioned kind the high voltage source which is preferably formed by a Marx generator is arranged laterally beside the microwave generator and in parallel relationship therewith so that the voltage outputs of the high voltage source, which are at the mutually remote ends of the Marx generator, can be connected to the axially mutually remote ends of the microwave generator. That ensures optimum dielectric strength. The maximum holding voltage of the microwave generator is determined by the external spacing of the two metallic elements.
In that known microwave generator the spark gap is oriented on its longitudinal axis, that is to say it is oriented axially.